The trend in microelectronics, as well as in micromechanics, is towards ever smaller dimensions. Some of the most interesting techniques for fabrication of micro and sub micro structures include different types of lithography.
Photolithography typically involves the steps of coating a substrate with a photoresist material to form a resist layer on a surface of the substrate. The resist layer is then exposed to radiation at selective portions, preferably by using a mask. Subsequent developing steps remove portions of the resist, thereby forming a pattern in the resist corresponding to the mask. The removal of resist portions exposes the substrate surface, which may be processed by e.g. etching, doping, or metallization. For fine scale replication, photolithography is limited by diffraction, which is dependent on the wavelength of the radiation used. For fabrication of structures on a scale of less than 50 nm, such a short wavelength is needed that the material requirements on the optical systems will be major.
An alternative technique is imprint technology. In an imprint lithography process, a substrate to be patterned is covered by a mouldable layer. A pattern to be transferred to the substrate is predefined in three dimensions on a stamp or template. The stamp is brought into contact with the mouldable layer, and the layer is softened, preferably by heating. The stamp is then pressed into the softened layer, thereby making an imprint of the stamp pattern in the mouldable layer. The layer is cooled down until it hardens to a satisfactory degree followed by detachment and removal of the stamp. An alternative method is to employ a radiation-curable polymer as the mouldable layer on the substrate. Such a material is typically liquid at room temperature, and may be spun on the substrate surface. The stamp is placed in contact with the mouldable layer to imprint the same, and the radiation-curable layer is subsequently exposed to radiation, typically UV radiation, either through the stamp or the substrate, at least one of which is transparent to UV radiation. Once the layer has cured, the stamp is separated from the substrate for subsequent processing of the substrate.
Separation of objects attached to each other in a sandwich structure in imprint lithography are typically separated in a manual process, by inserting a cutting edge into the periphery portion of the sandwich structure between the stamp and the substrate.